Metal drawing



June 22, 1954 HEMPEL 2,681,630

METAL DRAWING Filed Jan. 2, 1951 3 Sheets-Sheet l INVENTOR. Gustav A. Hempe/ a eM/%em/WM HIS AT TORNE Y5 J1me 1954 e. A. HEMPEL 2,681,630

METAL DRAWING Filed Jan. 2, 1951 5 Sheets-Sheet 2 x" I II H e B C XII lOc INVEN TOR.

Gustav A. Hempe/ HIS ATTORNEYS June 22, 1954 HEMPEL 2,681,630

METAL DRAWING Filed. Jan. 2, 1951 3 Sheets-Sheet 3 IOOOO I I I I I I I I l CURVE SHOWING RELATION 9000 of P to e 8000 Where: 2 P Required blank holding m 7000 force for force of E Of |bsl u g 6000 0=0utword-downword slope angle of cooperotmg or E opposed holddown and 5000 die surfaces. U) I a 5 o 4000 u.

3000 w n: 5; m 2000 In a: a.

II I000 9 in degrees SLOPE 0F DIE AND HOLDDOWN SURFACES IN DEGREES.

INVENTOR.

' Gustav A. Hempe/ HIS ATTQRNE Y5 Patented June 22, 1 954 UNITED STATEE OFFICE McDowell Manufacturing Company,

Millvale,

Pa., a corporation of Pennsylvania Application January 2, 1951, Serial No. 204,048

4 Claims.

The invention relates to metal drawing and particularly, to drawing metal blanks or sheets into hollow shapes or cups where relatively high blank-holding or gripping pressures are required or where shapes of odd or irregular contour are to be produced.

The usual metal drawing operation is performed in a press with a conventional die set which consists essentially of a female die, a holddown plate and a punch. The usual female die has a flat surface or draw face and a hollow cavity of a suiiicient size to permit the punch to force the blank therealong. The flat surface or draw face of the female die forms a plane which is at right angles to the perpendicular or draw axis and is usually as large or larger than the size of the blank which is to be drawn. In carrying out the operation a blank is placed on the draw face over the hollow cavity of the female die, if the die is used in a double action press. If the die is used in a single action press, the die is reversed and the punch and blank holder are on the bottom and the die with the cavity on top. Then, the blank is placed on the blank holder. A flat blank holder or holddown plate having a punch cavity through it in alignment with the cavity of the female die is mounted in the press and is positioned to hold the blank in compression on the die; and a male punch is advanced to form the blank by moving it into the die. A suflicient holding pressure must be provided by the blank holder Or holddown plate to prevent the blank from wrinkling and to cause the metal to flow as it is drawn into the female die by the punch. The punch furnishes sufficient pressure on the middle portion of the blank to push it into the cavity of the female die and thus draw it to the desired shape.

Since the maximum blank holding pressure on a drawing press is limited by its capacity, a definite problem has arisen in the present day art, particularly due to the need for producing products from relatively thin, higher tensile strength and hard metals with a minimum number of draws and also for producing odd shaped products. I have determined that the problem hinges to a great extent upon providing a more effective holddown pressure or force action on the blank fora given maximum available press pressure andessentially, upon means for better controlling and applying holddown pressure on the blank.

Even in drawing shallow shapes, the. blank must be gripped. tightly around its edge and b kd ng Pr e r uir s may be as h as two or three times the drawing pressure. If the blankholder is adjusted unevenly or loosely or if the holding force is insuii-lcient, wrinkles will appear around the shell. One wrinkle tends to lift the holder sufliciently to permit a group of wrinkles to start folding about the shape. It is thus important to apply an even and sufficient blank-holding action. In other words, the blank must have suilicient resistance to prevent wrin kling and yet permit the metal to flow about the draw ring. The blank-holding action is especially important where higher tensile strength and harder metals such as stainless steel are to be drawn, where odd shapes are to be produced, where relatively thin blanks are to be used, and where the diameter of the cup or shape to be produced is to be less than of the blank size. In general it may be stated that the limits in drawing the higher tensile strength and harder metals are found in the apparatus rather than in the material.

In an attempt to provide a better holddown action, draw beads have been formed from pieces or bars of hardened steel leaving a radius on the top face set in the fiat face or surface of the die to extend above such surface a distance substantially corresponding to the thickness of the blank to be drawn. To receive the draw bead radius that projects above the die surface, clearance is provided in the opposed surface of the blank holder. The height of the bead above the blank holder surface or face controls the holding resistance on the blank. In some instances, it is the practice in drawing rectangular shapes, to use draw beads only at the corners or near reverse bends in irregular shapes to hold back the metal. The draw bead method of increasing the blank-holding pressure eifect or resistance is very expensive and difficult to adjust. Not only is the draw bead costly to make, but its eiiective life is very short. It requires extensive trial and error experimentation as to location and dimensions and involves high repair and maintenance costs. It produces an undesirable deformation of the blank edge or flange. I have also experimented with a stepped die surface and other methods and found that they did not provide a practical solution to the problem here involved. Also, variation in the radius of the draw ring did not, in itself, solve it.

It has thus been an object of my invention to develop a practical solution to the problem or problems above outlined.

Another object has been to provide a new approach to the problem of increasing the efiection thereof.

such surface of the holder.

tive holddown pressure on a blank being drawn.

A further object has been to devise improved procedure or apparatus for drawing metal blanks.

A further object has been to provide an improved draw apparatus construction which will make practical the drawing of unusual or odd shapes from relatively thin, high tensile strength and hard metal blanks.

A still further object has been to provide means for better controlling the holddown action on a blank and to do so without offsetting disadvantageous effects.

These and many other objects of my invention will be apparent to those skilled in the art from the claims and the description of exemplary embodiments of my invention.

In the drawings:

Figure'l is a top plan view of a circular female die constructed in accordance with my invention;

Figure 1A is view similar to Figure l, but shows a somewhat rectangular female die constructed in accordance with my invention;

Figure 2 is a sectional elevation through apparatus employing my invention; it illustrates somewhat diagrammatically a preliminary positioning of its parts for drawing a blank and is taken along line IIII of Figure 1 or 1A;

Figure 3 is a view similar to Figure 2, but showing a holddown part in position on the blank and a punch part ready to initiate a drawing operation;

Figure 4 is a view similar to Figure 3, but shows the relationship of the blank and the parts at the completion of a drawing operation where a flange is to be provided;

Figure 5 is an enlargedsectional detail in elevation taken along the same section as Figures 2 to l, but showing a conventional draw apparatus during a drawing operation; it illustrates forces and components acting on the blank;

Figure 6 is a view similar to Figure 5, but showing apparatus employing my invention; it illustrates comparatively to'Figure 5, forces and 7 components set up in the blank;

Figure '7 is a graph plotted between die and holddown surface inclination and corresponding required. pressures on the holddown to illustrate the principles of my invention.

In accordance with my invention, the opposed or under surface of the blank holder, instead of being fiat, is outwardly declining in the general direction of a blank attenuating force application forming movement of a draw punch 52 and may be a portion of the surface of a circular cone, a sphere, an oval, a cylinder, or any combina- By way of example, the surface portion nearest the die cavity l la may be conical in shape, while the outer portion may be spherical in shape; or as shown in Figure 1A, the corner portions of a rectangular die H3 may beconical in shape and merge into substantially rectangular planar portions between the corners.

I'he apex or highest point of such surface is above or over the lip of the die cavity and the opposed die surface or face is made to match From the graph of Figure 7, it will be apparent that the required holddown pressure may be brought down toless than half the pressure required employing a conventional apparatus, or in other words, the

effective holding action of a given press may be more than doubled.

Employing my invention, I have been able to,

' for the first time, make highly satisfactory odd r Pz'forms the hollow cup or shape.

shapes or cups, and regardless of their shape, to draw products having highly improved overall characteristics. That is, I have been able to successfully employ blanks of thin, relatively hard metal to produce drawn products of cubical, cylindrical, conical, spherical, oval, or somewhat rectangular shapes, or of any combination of these and in general, any shape of practical application. Unusual shapes of containers, sinks, tubs, pans, etc. can be successfully produced in accordance with my invention.

Referring to the drawings, I show a female die it, a blank-holder ll, a punch l2, and a metal blank 13. Both the die ID and the blank-holder ll have been constructed in accordance with my invention and employ inclined curvilinear holding surfaces or faces.

The die part H), as shown, has a hollow draw bore Ina, a mounting flange lilb an outwardly-declining blank-holddown draw face or surface file, and a draw ring or punch entry mouth portion Hid. The inner boundary of the surface Etc terminates in an apex file and the outer bo undary in an offset or depressed edge ill). 7

The holddown part or blank-holder H, as shown, has a hollow bore Ha adapted to be aligned with the bore Illa and to by-pass the punch it. The part II has a mounting flange lib to position and hold it in a press and is hollowed out to provide a female, inclined, holding face or surface He that is substantially complementary with the opposed male surface We of the die and has an inner depressed edge He and an outer apex edge Hf.

The surface We lies in an outwardly declining plane that forms an angle 0 with the plane of force application, or in other words, a plane that is perpendicular to the direction of the force application. The opposed holding surface Hc forms the same angle 9 with such plane.

In Figure 1, a round or circular die cavity and in Figure 1A, a rectangular die cavity is shown.

Other die cavities have been used employing my invention for providing irregular or odd shaped products.

' The method for using this apparatus is quite simple, yet it achieves a very practical result in advancing the art. Figure 2 shows the relative positions of the die ill, blank-holder ll, punch 52, and blank l3 prior to commencing the draw. It will be noted that the blank '13 substantially centered over the die cavity 555a to rest upon the apex edge we of the inclined die face or surface iilc. Figure 3 shows the relative positions of the parts after blankeholding pressure or force P1 has been applied by the press to the blank-holder or holddown member H. The effect of the pressure or force P1 on the blank-holder It is to form the blank it into an inverted cone with a flat center surface or top.

Figure 4 shows the relative position of the apparatus parts and the shape of blank at the completion of a drawing operation. Ihe punch force Although I have illustrated only a single drawing opera- 7 tion, the principles of my inventionapply well to multiple operations where relatively deeper shapes are required. The shape shown inFigure 4 has a bottom wall I30. (which may be cut out if a hollow shape is desired), aside wall Hit of lesser thickness, and a lip I30 connecting the side wall to a thicker flange 13d.

I have found that by using an outwardly de- Jclining, properly shaped and sloped draw fa'ce lllc, it is now possible to more than double the holddown action on the blank 13 for a given available Dress force P1 and to do so without any offsetting undesirable effects or results. Shapes thus produced are free from wrinkles due to the circumferential stresses. I have also found that it is possible to draw much harder materials than hitherto possible because of the increased effective blank-holding action achieved by my invention. For example, I have found that by using an inclined surface of it is possible to use 25% less blank-holding force P1. For optimum results, I prefer to use an inclined surface of about 5 to 30. As will be noted from Figure 7, the maximum practical limitfor the surface slope is about 60. The minimum angle of decline is always less than 90 with respect to the axis of force application of the punch and as shown in Figure 6, from the direction of the axis of forming advance or force application of the punch. Thus, as shown, the declination is in the general direction of the draw-force application P2 or blank attenuation.

The improved drawing operation is achieved by taking advantage of two important force actions. Increased friction action results at B, see Figure 6, as the blank I3 is caused to pass around a more acute angle at the draw ring. The other action is a result of applying force P1 at an angle to the normal (i. e. other than at a right angle to the blank).

Using the old method and apparatus as shown in Figure 5, the forces acting on the blank will be different from those forces as shown in Figure 6. In Figure 5, the force P2 acting on the punch I2 is equal to the friction B acting on the bend (draw ring) plus the sliding friction F and F" of the top and bottom surfaces respectively of the blank. The sliding friction F and F is equal to the coefficient of friction of the respective surfaces, 1" and 1, times the force acting normal to the surface; namely P1 or N. F==f'P1 and F"=fN'. Assuming f':=,f", and as P1 is perpendicular to the blank under the blank-holder, P1 -=N'. The sliding friction therefore is equal to 2f'P1 or 2F. P2=B'+F'+F".

In Figure 6, I have shown the forces which act upon blank [3 where there are opposed inclined surfaces 100 and He (see Figure 2), instead of opposed horizontal flat surfaces, as shown in Figure 5. The force P2 acting on the punch I2 is equal to the sum of the friction B acting on the bend, the sliding friction F and F1 (top and bottom surfaces respectively of the blank), and, in addition, the components :c and an. Thus,

friction is equal to a constant force of 10,000 pounds, regardless of the amount of bend,

20,000=10,000+ (fN) +(J1N) +P1 sin 0N tan 6 Component y shown in Figure 6 is equal to force N=P1 cos 0. Thus:

20,000=l0,000+.5P1 cos 0+.5P1 cos 0+P1+sin 0+P1 cos 0 tan 0 P1 cos 0 (1+tan 0) +21 sin 0=10,000

1 cos 0 (1+tan 6) +sin 0 Table 0 cos 6 tan 0 l-i-tan (l (1 22 6) sin 0 P1 000 1. 000 l. 000 000 10, 000 176 1. 176 1. 157 174 7, 510 364 1. 364 1. 282 342 6, 150 577 1. 577 l. 365 500 5, 370 839 1. 839 1. 408 643 4, 870 50 643 1. 192 2. 192 1. 410 766 4, 600 60 500 1. 732 2. 732 l. 366 866 4, 490 70 342 2. 748 3. 748 1. 282 940 4, 500 174 5. 071 6. 671 1. 160 985 4, 670

For the purpose of illustration, I have kept the friction force B constant. This force, however,

will increase with the angle 0, thus also increasing the blank-holding effect.

Although I have exemplified certain embodiments of my invention for the purpose of illustration, it will be apparent that various modifications can be employed. For example, it is possible to combine conventional draw beads with opposed inclined surfaces to produce an even greater blank-holding elfect, although best results are obtained by opposed, substantially complementary, inclined surfaces, only. My invention can be successfully applied to any conventional press forming equipment whether it is of a single, double acting, or hydraulic type.

What I claim is:

1. An improved apparatus suitable for drawing a blank into an unusual blank shape with a minimum holddown force of greater effectiveness which comp-rises in combination, a draw die having a draw bore therein that is surmounted by a punch entry mouth portion, a draw punch positioned in operative association with said draw die for blank attenuating movement through said mouth portion into the draw-bore thereof, a blank-receiving draw face on said draw-die declining outwardly from said mouth portion, and a blank holddown member operatively positioned in an opposed relationship with said draw face, a holding face on said blank holddown member inclining outwardly in a substantially complementary manner and opposed relationship with said draw face to hold outer portions of the blank down in an outwardly declining manner along their full extent and in compression on said draw face during the blank attenuating movement of said draw punch through said mouth portion into the draw bore of said draw die.

2. An apparatus as defined in claim 11 wherein said draw face defines an angle of less than with respect to an axis of draw force application of said draw punch and in the direction of blank attenuating movement of said draw punch.

3. An improved apparatus for drawing a. metal blank into a wrinkle-free hollow shape of improved characteristics with a minimized required holding-down force of greater effectiveness which comprises in combination, a draw die having a draw bore therein that is surmounted by a punch entry mouth portion, said draw die having a blank-receiving draw face about and declining outwardly from said entry mouth portion to position the blank over said draw bore, a blank holddown having a bore in substantial alignment with said draw bore, said holddown being operatively positioned in an opposed relationship with said draw face and inclining outwardly in a substantially complementary manner with respect thereto to deform outer portions of the blank upon said draw face in an outwardly-declining manner about a central portion of the blank that is over said mouth portion and to hold the outer portions of the blank in compression on said draw face while the central portion thereof is being attenuated, a draw punch positioned in operative association with said draw die and holddown to move through the bore of said holddown upon and to attenuate the central portion of the blank through said entry mouth portion into said draw bore, and said draw face declining outwardly in the general direction of the blank attenuating movement of said draw punch.

4. An apparatus as defined in claim, 3 whereinv said draw face and said holddown each define 1 an outwardly declining angle of about 5 to 30 with respect to a plane transverse to an axis of draw force application of said drawn punch.

8 References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 601,738 Stampacchia i Apr. 5, 1898 760,921 Rigby May 24, 1904 909,342 Smith Jan. 12, 1909 1,245,059 Strand Oct. 30, 1917 1,375,305 Maisel Apr. 19, 1921 2,132,002 Hight Oct. 4, 1938 OTHER REFERENCES Page 220, Die Engineering Layouts and Formulas, Hinman, 1st edition, McGraw-Hill Book Co. Inc., New York, 1943. D 

